Blends of linear low density ethylene copolymers

ABSTRACT

Novel polymer blends are provided comprising a linear low density copolymer of ethylene with an olefin containing 4 to 10 carbon atoms (LLDPE) compounded with a minor amount of an at least partially isotactic, partially crystalline butene-1 polymer comprising at least about 80 wt. % of polymerized butene-1. The blends can be fabricated with better processability and reduced blocking into blown films having improved impact properties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to novel compositions comprising a linear lowdensity copolymer of ethylene and a minor amount of an olefin containing4 to 10 carbon atoms (LLDPE), and to films of improved properties formedfrom such compositions. Also included in the invention is the process offorming blown films from such compositions which is accomplished withimproved processability and less blocking.

2. Description of Related Art

The following information is disclosed in accordance with the terms of37 CFR 1.56, 1.97 and 1.98.

U.S. Pat. No. 4,565,847, issued Jan. 21, 1986 to S. K. Bahl et al.,discloses blends of LLDPE, polypropylene (PP) or ethylene-propylenecopolymer, and ethylene-propylene-diene monomer rubber (EPDM), which arestated to form films having improved MD tear strength and dart dropimpact properties.

U.S. Pat. No. 4,579,912, issued Apr. 1, 1986 to P. J. Canterino et al.,teaches blends of LLDPE and an aromatic polymer, e.g., polystyrene,which are stated to form films of improved MD tear strength and higherstiffness compared to LLDPE alone.

U.S. Pat. No. 4,657,982, issued Apr. 14, 1987 to A. K. Breck et al.,discloses film-forming blends of a linear copolymer of ethylene and a C₄to C₈ alpha-olefin, and two "polybutenes," one having a number averagemolecular weight of 500 to 1500 and the other a number average molecularweight of 1700 to 10,000.

U.S. Pat. No. 4,456,660, issued June 26, 1984 to E.A. Columbo, teachesblends of conventional branched low density polyethylene (LDPE) andpolybutene-1 used to prepare laminated films with unblended LDPE whichare stated to be tough and to have good tear resistance.

U.S. Pat. No. 3,660,530 issued May 2, 1972 to Hoblit et al., disclosesblends of high density polyethylene and block copolymers of polyethyleneand a polymer of butene-1 which are stated to have improved stress crackresistance.

SUMMARY OF THE INVENTION

In accordance with this invention, novel polymer blends are providedcomprising a linear low density copolymer of ethylene with an olefincontaining 4 to 10 carbon atoms (LLDPE), compounded with a minor amountof an at least partially isotactic, partially crystalline butene-1polymer comprising at least about 80 wt. % of polymerized butene-1. Theblends can be fabricated with better processability and reduced blockinginto blown films having improved impact properties.

DESCRIPTION OF PREFERRED EMBODIMENTS

The linear low density ethylene copolymers (LLDPE) of this invention arelinear copolymers of ethylene and a minor amount, preferably about 2 to10 wt. %, of an olefin, preferably a 1-olefin, containing 4 to 10 carbonatoms and having a density of about 0.9 to 0.94, a melting point ofabout 110° to 130° C., and a melt index of about 0.2 to 10. Thepreferred olefin comonomers are 1-butene, 1-hexene and 1-octene. TheLLDPE may be prepared by any of various methods known in the art, e.g.,by relatively low pressure methods as disclosed, for example, in U.S.Pat. No. 4,076,698, or by relatively high pressure methods, asdisclosed, for example, in U.S. Pat. Nos. 4,405,774 and 4,530,983.

The butene-1 polymers contemplated under this invention are at leastpartially isotactic, partially crystalline polymers comprising at least80 wt. %, preferably at least 90 wt. % of polymerized butene-1. Thesepolymers include homopolymers of butene-1 and copolymers of at leastabout 80 wt. % of butene-1 and up to about 20 wt. % of at least onepolymerized comonomer, e.g., an olefin, preferably a 1-olefin,containing 2 to about 10 carbon atoms, and preferably have a numberaverage molecular weight of at least about 25,000, a density of fromabout 0.890 to 0.920, and a melt index of from about 0.1 to 40, (ASTMcondition E). Some of these polymers are described in the article on"Polymers of Higher Olefins" in Kirk-Othmer, Encyclopedia of ChemicalTechnology, Third Edition, Vol. 16, Wiley-Interscience, 1981, pages470-477. The polymers may be prepared using a Ziegler-Natta typecatalyst as described for example in U.S. Pat. No. 3,362,940 or theforegoing Kirk-Othmer article. In general, the butene-1 polymers inunblended form are capable of being formed into shaped articles such asfilms.

The blends of LLDPE and butene-1 polymer may be prepared using any ofvarious methods known in the art. For example, pellets of the twopolymers may be dry blended and the blend added directly to a blown filmextruder, e.g., a Sterling extruder, to produce films having athickness, for example, of about 0.5 to 5 mils.

The polymer blends of this invention contain a minor amount, i.e., under50 wt. % of the butene-1 polymer based on the combined weight of LLDPEand butene-1 polymer. Preferably, the blend contains about 1 to 25 wt.%, more preferably, about 2 to 10 wt. % of butene-1 polymer, based onthe combined weight of LLPDE and butene-1 polymer. In addition to thepolymer components, the blend may also contain any of various additivesconventionally added to polymer compositions for different purposes,e.g. lubricants such as microtalc, stabilizers, compatibilizers,pigments, etc.

The following examples further illustrate the invention.

COMPARATIVE EXAMPLES A and B AND EXAMPLES 1 to 4

Films of 1.0 and 1.5 mils nominal gauge thickness were prepared fromMobil NTA-101 LLDPE, which is a linear low density copolymer of ethyleneand about 6 wt. % of 1-hexene having a density of about 0.918, a meltingpoint of about 125° C. and a melt index of about 1 (Comparative ExamplesA and B), the foregoing Mobil NTA-101 blended with 5 wt. % of ShellDP8310, which is a copolymer of about 94 wt. % of polymerized butene-1and about 6 wt. % of polymerized ethylene, having a density of about0.895, a melt index of about 3.0 and a number average molecular weightof about 50,000 (Examples 1 and 2), and the foregoing Mobil NTA-101blended with 5 wt. % of Shell PBO400 polybutene-1 (a butene-1homopolymer) having a density of about 0.915, a melt index of about 20,and a number average molecular weight of about 40,000 (Examples 3 and4). The polymer blends of Examples 1 to 4 were prepared by dry blendingthe pellets and the wt. % of butene-1 polymer in these blends was basedon the combined weight of the two polymers. The Mobil NTA-101 LLDPE ineach of the examples contained 5000 ppm of microtalc.

The films were made in a 21/2 inch Sterling blown film extruder underthe following fabrication conditions: BUR (blow up ratio) of 2.5,production rate of 150 lb/hr, die gap of 80 mils, and a 6 inch die.

The table shows the RPM, screw tip pressure and screw amperes at whichthe extruder operated and, the Spencer Impact (ASTM D3420), Dart DropF₅₀ Impact (ASTM D1709), and Induced Blocking Force (ASTM D3354) of thefilms prepared in the various examples.

                                      TABLE                                       __________________________________________________________________________             Screw              Dart                                                       Tip      Nominal                                                                            Spencer                                                                            Drop                                                                              Induced                                                Press.                                                                            Screw                                                                              Gauge                                                                              Impact                                                                             F.sub.50                                                                          Blocking                                      Example                                                                            RPM psig                                                                              Amperes                                                                            mils gms/mil                                                                            gms gms                                           __________________________________________________________________________    A    67.4                                                                              3090                                                                              46   1.0   763 175 85.1                                          B    67.4                                                                              3090                                                                              46   1.5   633 238 76.6                                          1    87.0                                                                              2650                                                                              31   1.0  1780 206 68.2                                          2    87.0                                                                              2650                                                                              31   1.5  1330 256 54.8                                          3    95.9                                                                              2680                                                                              29.5 1.0  1770 210 62.9                                          4    95.9                                                                              2680                                                                              29.5 1.5   924 256 39.9                                          __________________________________________________________________________

The results shown in the table indicate that improved Spencer Impact,Dart Drop Impact and antiblocking properties were obtained with thefilms of Examples 1 to 4 prepared from blends of LLDPE with 5% of abutene-1 polymer as previously defined, as compared with the films ofComparative Examples A and B of equivalent thickness prepared from thesame LLDPE not containing any butene-1 polymer. Moreover, these improvedproperties were accompanied by a superiority of processability inproducing the butene-1 polymer containing films of Examples 1 to 4 ascompared with the films of Comparative Examples A and B, indicated bylower values of screw tip pressure and screw amperes.

I claim:
 1. A polymer blend comprising polymers consisting of a linearlow density copolymer of ethylene with an olefin containing 4 to 10carbon atoms and about 2 to 10 wt. % of an at least partially isotactic,partially crystalline butene-1 polymer comprising at least about 80 wt.% of polymerized butene-1.
 2. The blend of claim 1 wherein said ethylenecopolymer contains about 2 to 10 wt. % of said olefin in polymerizedform.
 3. The blend of claim 1 wherein said olefin is a 1-olefin.
 4. Theblend of claim 3 wherein said 1-olefin is 1-butene, 1-hexene, or1-octene.
 5. The blend of claim 1 wherein said ethylene copolymer has adensity of about 0.9 to 0.94, a melting point of about 110° to 130° C.,and a melt index of about 0.2 to
 10. 6. The blend of claim 1 whereinsaid butene-1 polymer has a number average molecular weight of at leastabout 25,000.
 7. The blend of claim 6 wherein said butene-1 polymer is ahomopolymer of butene-1.
 8. The blend of claim 6 wherein said butene-1polymer is a copolymer of butene-1 and ethylene.
 9. The blend of claim 1wherein said butene-1 polymer has a density of from about 0.890 to 0.920and a melt index of from about 0.1 to
 40. 10. A film composed of theblend of claim
 1. 11. A film composed of the blend of claim
 4. 12. Afilm composed of the blend of claim
 6. 13. A film composed of the blendof claim
 5. 14. A process of extruding the blend of claim 1 into a blownfilm.
 15. A process of extruding the blend of claim 4 into a blown film.16. A process of extruding the blend of claim 6 into a blown film. 17.The blend of claim 1 wherein said butene-1 polymer in unblended form iscapable of being formed into shaped articles.